The present invention relates to a method of determining the distance between two sound generating objects to subsequently feed the objects with adapted audio signals. This may be used in order to e.g. provide a user with realistic 3D sound.
A usual manner of providing such sound is to adapt an audio signal on the basis of a Head Related Transfer Function selected for the particular user or distance.
The scientific literature on the subject of personalizing generic HRTF data is comprehensive. In general, the methods can be divided into 4 subcategories                1) Measure the HRTF's from a limited number of angles and apply this information to a generic HRTF database        2) Measure some physical properties like ear size and head size and adding this information to the generic HRTF database.        3) Take an image of the head and adding information from the image to the generic HRTF database.        4) Adjust or select the HRTF database based on user responses like e.g. listening tests.        
Different manners of determining a HRTF may be seen in: U.S. Pat. Nos. 6,181,800, 6,768,798, 7,840,019 and US2013/177166.